Field of the Invention
The present invention relates to a printer for use in printing characters on a sheet, such as a slip.
Description of the Prior Art
Conventionally there is a slip printer which prints characters on a sheet such as a slip as disclosed in JPU No. 62-150148 and JPY 2-8781.
In such a printer, a printing mechanism, a sheet feed mechanism, and a driving mechanism of the sheet feed mechanism are respectively mounted on a chassis, wherein one of feed rollers of the sheet feed mechanism is attached to a swing arm and a gap defined between the feed rollers is adjusted depending on a thickness of a sheet. There has been employed a method for transmitting torque from the chassis side to the feed rollers attached to the swing arm by way of a gear train. In such a case, when the inclination angle of the swing arm is changed depending on the thickness of a sheet, an interval between a shaft of the gear train on the chassis and a shaft of the swing arm is changed, which leads to a change of backlash of the gears. As a result, there is a drawback in that the feeding amount of the sheet is changed.
Since the gear train for transmitting torque from the chassis side to the feed rollers attached to the swing arm extends over two members, it causes a drawback in that the sheet feed mechanism is complex and adjustment of meshing of the gears is troublesome in assembling the printer.
Further, as exemplified in the printer disclosed in JPU No. 62-150148, driving rollers and driven roller constituting the sheet feed mechanism are disposed at a front side of the printing mechanism, namely, at the discharge side of the slip since the slip printer can print characters on the slip to an extent of an end portion thereof in the longitudinal direction thereof, namely, in a feeding direction. Accordingly, in installing an ink ribbon cassette, both arm portions of the ink ribbon cassette need to be moved from the sheet feed mechanism to the printing mechanism so as to insert an ink ribbon through a narrow gap portion defined between a print head and a platen of the printing mechanism. As is well known, an ink ribbon is soft and extends over arm portions of the ink ribbon cassette and can be freely drawn out. There is a possibility that such an ink ribbon is caught by an end of a frame or a concave or convex portion formed in a tip end of the print head, etc., and it is troublesome to install or remove the ink ribbon cassette in a conventional printer having the sheet feed mechanism or the printing mechanism exposed. If the ink ribbon is picked up by a hand so as to be led between the print head and the platen, the hands are made dirty. Even if the ink ribbon cassette is installed, there is another problem in that it is difficult to confirm whether the ink ribbon cassette is appropriately positioned or not.
If printing is performed in a state where the ink ribbon is loosened while it remains caught by the frame etc., there is a likelihood that the ink ribbon is rammed between a print head and a document table, which prevents normal feed of a slip, resulting in a feed failure or a paper jam. Further, if such problem occurs, there is a drawback in that it is difficult to confirm such problem.